The present invention relates to a method and a device for dividing up a total amount of fuel, which is to be injected into a combustion chamber of a cylinder during a combustion cycle, into a plurality of injections, as well as a method and a device for dividing up a total amount of fuel, which is to be injected into a combustion chamber of a cylinder during a combustion cycle and includes a first amount of fuel, a second amount of fuel, and a third amount of fuel, into a first injection, a second injection, and a third injection of the combustion cycle of the cylinder.
In common-rail injection systems for internal combustion engines, a high-pressure pump is used to build up a pressure of up to 2000 bar in a pressure chamber, which contains the fuel to be injected and is referred to as the common rail. The common rail is connected to all of the injection devices of all engine cylinders. Metering valves, usually solenoid valves or piezoelectric systems, are used as injection devices, through which fuel is injected into the combustion chamber of the cylinder, when they are in the open state.
In contrast to direct-injection systems, in which a pressure must be built up anew for each combustion cycle or injection cycle of each cylinder, the pressure in the common rail of the common-rail injection system remains in a constant range, regardless of the combustion sequence.
Since this high-pressure is applied to all of the solenoid valves of all engine cylinders, the fuel can therefore be injected into the combustion chambers of the cylinders, by controlling the opening of the respective solenoid valve in a simple manner, i.e. by controlling a lift, an opening and/or closing time, and an opening and/or closing speed of the solenoid valve.
However, the high pressure in the combustion chamber, up to 160 bar, and the speed at which the pressure increases during combustion cause these direct-injection systems and common-rail injection systems to be very loud.
In order to reduce the noise emissions, pre-injection is implemented in common-rail systems. In this context, a small amount of fuel is injected into the combustion chamber of the cylinder and ignited up to a few milliseconds prior to the main injection. This preheats the combustion chamber and creates improved conditions in the combustion chamber for the main combustion during the main injection.
In this regard, DE 198 60 398 proposes the implementation of a pre-injection, a main injection, and/or a post-injection, which can be divided up into a plurality of pre-injections, main injections, and/or post-injections, respectively.
U.S. Pat. No. 5,402,760 describes a fuel-injection control device, which provides various control-current waveforms for a solenoid valve, in order to minimize the effects of residual magnetic flux in this valve.
However, the mutual dependence of the injection amount and the injection times causes the individual injections of a combustion cycle in the described injection systems to affect each other. This can result, for example, in injection amounts not adjusted to each other being injected in the respective injection occurrences of a combustion cycle, or in control starting points not adapted to the specific injection amounts being used for the individual injection occurrences. This results in irregular combustion, along with unacceptable pressure gradients in the engine, which in turn lead to an increase in the noise and pollutant emissions.
The present invention is based on the problem of reducing noise emissions and pollutant emissions of the internal combustion engine.
This problem is solved by the features specified in claims 1, and 7, 12, and 13.
The advantages attained by the features listed in claim 1 include, in particular, that the amount of fuel for the last of the three injections of a combustion cycle does not fall below a minimum value. In this manner, it is ensured that, during the third injection of the combustion, sufficient fuel is supplied for satisfactory combustion, and therefore, a sudden drop in the combustion intensity due to insufficient fuel supply is prevented in the third injection. This advantageously prevents a sudden fall in the magnitude of the torque of the cylinder in relation to the total torque of the internal combustion engine. Consequently, a smoother characteristic curve of the pressure gradient in the engine, i.e. a characteristic not having, for example, a sharp fall, is attained. This ensures reduced noise and pollutant emissions.
An advantageous refinement of the present invention is specified in claim 2. The refinement according to claim 2 advantageously allows the fuel amount to be exactly determined, since the third fuel amount is calculated by subtracting the ascertained, first fuel amount, which is to be injected into the combustion chamber of the cylinder during a first injection of the combustion cycle, from the total fuel amount that is to be injected into the combustion chamber of the cylinder during a combustion cycle. Since the third fuel amount is calculated by simple subtraction, this refinement allows the computational time for the individual fuel amounts to be minimized.
A further advantageous refinement of the present invention according to claim 1 is specified in claim 3. The refinement according to claim 3 advantageously prevents a double calculation of the fuel amounts, since the total fuel amount is initially calculated, then the first fuel amount, then a second fuel amount that is to be injected into the combustion chamber of the cylinder during a second injection of the combustion cycle, and then the third fuel amount is calculated as a function of the three previously determined quantities. Therefore, the first injection has priority over the second injection.
The advantages attained by the features of claim 7 include, in particular, that the first position for the first injection and the second position for the second injection are checked in light of first limiting values and second limiting values, before the injections are carried out. This ensures that the injections are executed in the correct position, so that the individual injection occurrences do not mutually affect each other in a disadvantageous manner.
Further advantageous developments of the present invention ensue from the dependent claims.